The present invention relates generally to an illumination control for a projection display system and, more particularly, to a projection system illumination module for controlling the intensity of light from a discharge lamp through controlling polarization of the light beam.
In many projection display systems, a discharge lamp is used as the preferable light source. During operation it sometimes becomes desirable, or necessary, to control the intensity of the light from the discharge lamp in order to reduce the screen brightness, or to control the illumination level in response to reductions in the video output to improve the apparent contrast ratio of the system in dark or black scenes. Various attempts have been made to incorporate light intensity controls for discharge lamps by the use of devices inside the projector. However, such xe2x80x9cwithin the projectorxe2x80x9d systems have not yet been perfected to be satisfactory in the control of the intensity of lights from a discharge lamp, especially a high-pressure mercury discharge lamp which is a preferred light source for projection display systems. Some attempts to utilize a xe2x80x9cwithin the projectorxe2x80x9d system have been found to have a deleterious effect on the uniformity of the light distribution to the display device which limits the possible physical location of such a system within the projector. Other xe2x80x9cwithin the projectorxe2x80x9d systems require motors or actuators which may not be able to respond quickly enough to changes in video signals, especially when dynamic dimming is desired. In addition, such systems absorb input radiation and become hot. Accordingly, these xe2x80x9cwithin the projectorxe2x80x9d control system require careful thermal designs and are limited by such thermal requirements.
The present invention is directed to overcoming one or more of the problems or disadvantages associated with the relevant technology.
In the preferred embodiment of this invention, the light intensity is controlled outside of the projection system optics by means of an electronically controlled illumination module that may be used with any projection system. Such a system does not require motors or actuators to operate and, accordingly, is able to respond quickly to changes in the video signal if dynamic dimming is desired. In addition, the illumination module of this invention will not absorb input radiation and, therefore, is not subjected to thermal changes which can effect reliable operation, especially for static dimming.
By positioning the illumination module of this invention outside the projection system optics, the illumination module may be used to control the intensity of light with any projection system, and eliminates any potential thermal problems occasioned by overheating components. Because the illumination module control of the present invention is completely electronic, response time to video signal level changes is extremely short, so that the illumination control system can respond quickly if dynamic dimming is desired.
The illumination module of the present invention has no mechanical elements and no moving parts, but utilizes a polarizing beam splitter to split the light beam from the projection lamp into two polarization states, selectively altering the state of each polarized light beam to reject a controlled portion of the light before the selectively altered beams are recombined and passed to the display projection optics. This system is especially effective for controlling dynamic dimming.